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March 10, 2012

Another nail in the Aryan coffin

A new paper refutes the large-scale migration version of the Aryan theory

The Aryan theory has gone through many revisions: Historians and archaeologists like A L Basham and Mortimer Wheeler advocated an invasion theory where invaders triumphed over the natives due their military prowess and superior weapons. These invaders originated in Central Asia: one branch migrated to Europe and the other to Iran, eventually reaching India. By the time of historian Romila Thapar, the invasion theory morphed into a migration theory. According to Ms Thapar there is no evidence of large scale invasion, but migrations by Indo-Aryan speakers who bought their language and culture to India.

Though the theory changed, two factors remained constant: the existence of two separate groups (Dravidians and Aryans) and their identification as natives and foreigners. The scholarly consensus is that the Indo-Aryan speakers arrived in North-East India following the decline of the Harappan civilisation. These horse riding migrants introduced Vedic religion and Sanskrit language and culturally transformed a region bigger than ancient Mesopotamia and Egypt combined, non-violently.

Now a new paper published in the American Journal of Human Genetics states that current Indian population is derived from two ancestral populations—the Ancestral North Indians (ANI) and Ancestral South Indians (ASI)—both of which are older than 3500 Years Before Present (YBP). Though this seems to confirm the Aryan-Dravidian divide and the migration which happened after 1900 BCE, the paper actually does the opposite; it refutes the large scale migration version of the Aryan theory.

Researchers led by Mait Metspalu of Evolutionary Biology Group of Estonia studied 600,000 Single Nucleotide Polymorphism (SNP) markers among 30 ethnic groups in India. The human genomes consists of chromosomes, represented by the double helix and specific locations on the chromosome can be identified using markers with the common ones being micro-satellite markers and SNP markers. Among the two, SNP markers are popular for gene fine mapping. The study takes data from existing genetic studies and combines it with new data from North Indian and South Indian population to trace the external influences from Europe.

One of the ancestral components—the ANI—is common not just in South Asia, but also in West Asia and Caucasus while the ASI is limited to South Asia. While this may seem to clearly demarcate the natives and the foreign migrants, it does not. Except for some Astroasiatic tribes and two small Dravidian tribes in Tamil Nadu and Kerala, all other South Indians have more than 40% of the ANI component. This means that everyone except these few groups are not purely native.

The important question then is this: When did the ANI mix with the ASI?. If that period is between 1900 BCE and 1500 BCE, then it would confirm the many versions of Aryan theory in existence right now. When these researchers modeled the data, they could not find any evidence of a dramatic Central Asian migration for this period. So they went back and till about 12500 Years Before Present (YBP) they could not find any evidence. Thus the mixing of the ANI and ASI did not happen 140 generations before as was believed, but probably more than 500 generations back (Each generation is 25 years). The paper explicitly mentions Max Muller’s theory and says that it is hard to find evidence for such a migration following the collapse of the Harappan civilization.

Few years back, researchers working on this project suggested that the ANI emerged 40,000 years back and mixed with the ASI at a later date. So as it stands now, the mixing between the two groups happened some time between 40,000 YBP and 12,500 YBP. So if there is a European component in Indian genes, that event happened much earlier than the decline of the Harappan civilisation and not because of the hypothetical Aryan migration around 1500 BCE.

Going back 12,500 years we have to wonder what event was responsible for this shared ancestry between the ANI and Europeans? Did it happen during the Out of Africa migration phase? Humans reached India first before moving to Europe in which case the European gene pool would be derived from the much diverse South Asian pool. Or was there any other incident much later which was responsible for this?

Coming back to the period following the decline of the Harappan civilisation there are more questions for scholarly head scratching. Even though the ANI-ASI mixture may happened quite earlier, there must have been constant migration of people in both directions which was not large enough to leave a genetic footprint. If you accept that premise, how did this minor trickle of people change the region culturally. If these are the people who bought horses to India, why don’t we see a proliferation of horse bones following this period?

The current models don’t have a convincing explanation for many such questions.


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